The broad objective of the research is to obtain a basic understanding of endocrine changes occurring during sexual maturation of the rhesus monkey. The following are the major specific objectives and the experiments conducted thus far which relate to the objectives: a) Determination of the immunologic, physicochemical, and biologic properties of LH in serum of infant monkeys (in collaboration with Peckham, U. of Pittsburgh). Circulating LH, determined by one radioimmunoassay for monkey LH (0-0 system), is extremely high in both sexes during infancy. The concentrations decrease and approach those of the adult by 6 months of age. These increased concentrations are not observed when another radioimmunoassay for monkey LH (hCG-Rh) is used. The discrepancy between these two systems is being further investigated by methods which will provide insight into the physicochemical and biologic properties of the substance in infant serum. b) Determination of the period when negative feedback action of gonadal steroids on LH secretion becomes established. Results of measurement of serum LH (by the 0-0 radioimmunoassay) in monkeys castrated shortly after birth indicate that the relatively abrupt rise in circulating LH to castrate levels occurs at a critical weight (4 kg) rather than at a particular age (range 18-38 months). c) Determination of the onset normal luteal phases. Measurement of circulating progesterone and LH during the first 10 menstrual cycles indicate the initial cycles following menarche are anovulatory. Subsequently cycles occur which contain a short luteal phase (8-10 days). By the seventh cycle after menarche normal luteal phases (15-17 days) are observed. BIBLIOGRAPHIC REFERENCES: Foster, D.L., Lemons, J.A., Jaffe, R.B., and Niswender, G.D.: Sequential patterns of circulating LH and FSH in female sheep from early postnatal life through the first estrous cycles. Endocrinology 97:957, 1975. Karsch, F.J., and Foster, D.L.: Sexual differentiation of the mechanism controlling the preovulatory discharge of luteinizing hormone in sheep. Endocrinology 97:373, 1975.